1. Filed of the Invention
This invention relates to a stereoscopic microscope applied, for example, to the observation optical system of an ophthalmic slit lamp, and in particular to a stereoscopic microscope with a Galilean magnification changer.
2. Description of the Prior Art
The Galilean microscope and the binocular microscope have heretofore been widely used for the optical system of the magnification changer of this type. In the binocular microscope, entirely discrete two left and right microscopic optical systems are disposed so as to intersect each other at a predetermined angle, e.g., 10.degree.-12.degree., and therefore, the problem of the vergence of the eyes does not occur. In this optical system, however, the objective lens is divided into two, that is, a pair of objective lenses are present and therefore, when interchanging the objective lenses for the purpose of magnification change, the handling thereof is complicated and cumbersome. Also, no part of the light beam becomes a parallel light and therefore, it is difficult to divide the optical paths of the side view mirror, the camera, etc. from half-way of the barrel.
On the other hand, the Galilean microscope is provided with a single objective lens and a pair of eyepieces, and the light beams passing through the eyepieces into the two eyes of the observer are parallel to each other and therefore, the angle of vergence is zero, while when observing with the microscope removed, the angle of vergence has a predetermined value and differs between the time when observation is effected through the microscope and the time when observation is effected without the intermediary of the microscope. Thus, with the Galilean microscope it is difficult to view stereoscopically. In this optical system, however, the light beam from a point on the subject body can be made into a parallel light beam by the objective lens and therefore, the magnification change of the optical system including a zoom optical system becomes simple, and also various accessories can be mounted by inserting a beam splitter into the parallel light beam portion.
Now, as a Galilean stereoscopic microscope in which vergence is taken into consideration, there is known one in which wedge prisms are disposed outside the eyepieces as proposed in Japanese Utility Model Publication No. 19530/1983, but in this type of microscope, prisms are present between the eyepieces and the examiner's eyes and this leads to a disadvantage that the examiner's eye points, i.e., pupil positions, become too near to the prisms to see, and also offers a problem in that chromatic aberration and astigmatism occur.